Micromachines are extremely small machines with potential for utilization in fields such as micromechanics, biology and chemistry. They require very minutely structured actuator elements for their operation. Ordinary actuating devices of the electric power driven type require wiring or the like and are therefore not suitable for miniaturization. However, optical actuators driven by external stimuli utilizing photoirradiation can be configured to have integrated sensor and drive units, and since this advantageously eliminates the need for wiring or the like, actuator miniaturization is possible. Patent Reference No. 1 teaches an actuator element that utilizes voltage produced by an element exhibiting a photovoltaic effect on photoirradiation to enable movement of the actuator by the static electric force produced by the voltage. However, micro-level size reduction of the constituent element is difficult. Patent Reference No. 2 teaches an actuator element that utilizes an optical fiber, which is of simple structure and can also be micro-sized. However, the need to connect a light source to the actuator makes configuration of a tiny structure difficult.
Among the reported electrically driven actuators that do not require wiring are some that use ionic polymer film. Patent Reference No. 3 teaches driving of a polymer film by application of a voltage in a mixed solution of water and a polar organic solvent. However, this works only in a liquid and does not function in a dry system.
Patent Reference No. 4 teaches a chemo-mechanical material that produces mechanical deformation by chemical change of an organic compound, but the material has problems regarding response and weak force generation. Patent Reference No. 5 teaches use of a polydiacetylene compound exhibiting phase change on photoirradiation as a light-driven micro-actuator, but reversible photoinduced phase change is possible only in a specific temperature region and the efficiency of the photoinduced phase change is very low, so that repeated use is difficult.
A compound that reversibly forms two structural isomers of different color on irradiation with light is called a photochromic compound. The inventors propose diarylethene as a class of excellent compounds exhibiting photochromism. As set out in Non-Patent Reference No. 1 authored by the present inventors, diarylethene derivatives (diarylethene compounds) are characterized by excellent repetition durability in photoisomerization and stability of both isomers formed. In addition, as set out in Non-Patent Reference No. 2, also authored by the present inventors, derivatives that exhibit photochromism in the crystalline phase were also found, and application to optical recording materials and display materials is under study. Further, the inventors discovered that 1,2-bis(5-methyl-2-phenyl-4-thiazolyl)perfluorocylopentene mentioned in Patent Reference No. 6 is a diarylethene compound having a thiazole ring at the aryl position and is characterized by having higher stability than a diarylethene compound having thiophene at the aryl position. However, crystalline photochromism of this compound has not been reported.    [Patent Reference No. 1]: Japanese Patent Application Publication No. 2001-145379    [Patent Reference No. 2]: Japanese Patent Application Publication No. H5-180148    [Patent Reference No. 3]: Japanese Patent Application Publication No. 2006-54951    [Patent Reference No. 4]: Japanese Patent Application Publication No. H8-86272    [Patent Reference No. 5]: Japanese Patent Application Publication No. 2001-232600    [Patent Reference No. 6]: Japanese Patent Application Publication No. H10-45732    [Non-Patent Reference No. 1]: Chem. Rev., 100, 1685-1716 (2000).    [Non-Patent Reference No. 2]: Bull. Chem. Soc. Jpn., 77, 195-210 (2004).